1. Field of the Invention
This invention relates to a conversion device for converting the rotational motion of a motor shaft into a reciprocating motion and, more specifically, to a conversion device that utilizes an eccentric hub disposed between the motor and the output assembly.
2. Description of the Prior Art
The ballast underlying a railroad track must be compressed during the installation of new track or repairing old track. The typical means for compressing the railroad track ballast is to vibrate and/or tamp the ballast using a tamping machine. A tamping machine typically consists of two pairs of tamping tools connected to a common vibrating device. The vibrating device causes the tamping tools to oscillate rapidly about the axis of an output shaft. This vibration allows the tamping tools to penetrate the ballast bed. The vibration device operates by imparting a vibration into the ballast particles. This vibration creates a liquidification of the particles thereby allowing the tamping tools to move into the ballast. The tools then move in a squeezing motion to compact the ballast into a closely packed mass that is better able to support the track structure.
There is, therefore, a need for a conversion device for converting the rotational motion of a motor shaft into a reciprocating motion in an output assembly.
There is a further need for an assembly for converting a rotational motion along a first axis to a reciprocating rotational motion along an axis perpendicular to the first axis.
These needs and others are satisfied by the invention which provides for a conversion device having an eccentric hub disposed at the connection between a motor and the output assembly. The eccentric hub is generally cup-shaped and includes a circular sidewall having an inner bearing surface and an outer bearing surface. The sidewall has a thin portion and a thick portion disposed generally 180 degrees apart. The sidewall gradually decreases in thickness between the thick portion and the thin portion. The eccentric hub is coupled to a rotating output axle on the motor.
The output assembly includes a yoke and a shaft. The yoke includes a shaft that has an axis that is, preferably, about perpendicular to the axis of the output assembly shaft. The yoke shaft is pivotably coupled to the output shaft by a pivot pin that extends perpendicular to the axis of the output shaft and perpendicular to the yoke shaft. The output assembly shaft is coupled to a frame and may rotate axially, but is restrained from moving in an axial direction.
The output assembly shaft is generally perpendicular to the motor shaft. The yoke shaft is disposed within, and is coupled to, the eccentric hub. Thus, when the motor is actuated, the eccentric hub rotates. As the thick side of the side wall moves around the hub, the yoke shaft moves in response to the eccentric shape. One component of the yoke shaft""s motion is, in turn, imparted to the output assembly shaft. That is, the eccentric shape of the hub moves the yoke shaft in directions both parallel and perpendicular to the output shaft axis. The parallel component of this motion is not transferred to the output shaft as the yoke pivot pin allows the yoke shaft to pivot in the axial direction of the output assembly shaft. Thus, the only component of the yoke motion transferred to the output shaft is the horizontal component. This motion causes the output shaft to move in a reciprocal rotational motion about the output assembly shaft axis.
It is an object of this invention to provide a device for converting the rotational motion of a motor shaft to a reciprocal motion in an output assembly.
It is a further object of this invention to provide a device for converting the rotational motion of a motor shaft to a reciprocal motion in an output assembly that includes an eccentric hub.